@ Photon - I agree. For me its Amiga music that sounds like SID music ie. it sounds like the tones are actually being generated by the sound chip (like with C64 sound) and not just being played by the sound chip (what actually happens with Amiga sound).
But going back to goto80's original point I've got no idea really when the first use of the term chiptune was. The first time I remember encountering the distinction was in Timecircle's Draconian music demo where they make the distinction between "short synthetic" and "long sampled" Amiga music.